Details of Pliocene sequences resolved on a 3-D data set, central North Sea

The paper presents a sequence stratigraphic study based on 3-D seismic data, well-logs and conventional seismic sections. Three Pliocene sequences from the central North Sea are analysed. The 3-D seismic data allow detailed analyses of the spatial development and detailed description of the geometry of the systems tracts. On conventional seismic sections the sequences can be subdivided into two seismic units, separated by a downlap surface (maximum flooding surface). On 3-D seismic data the lower unit can be subdivided into an early lowstand, a late lowstand and a transgressive systems tract. Sequence boundaries are easily identified as continuous horizons on the Cosine of Phase display, which also enhances reflection terminations. Upper parts of sequences are associated with high values of reflection strength. Amplitude maps of the upper sequence boundary reflect amplitude tuning related to onlapping reflectors. The offlap break seems to be located landward of a zone with high amplitude values, reflecting densely spaced onlaps onto the upper part of the progradational front. Maps of the reflection intensity (a volume related attribute) may be interpreted as reflecting sediment facies distributions. Low values are related to transgressive and condensed fine-grained deposits, while higher values appear in the upper parts of prograding lowstand and highstand deposits, possibly related to the more coarse-grained sediments. These maps may thus contribute to the sequence stratigraphic interpretation of conventional data.